Field of the Invention
The invention generally relates to synchronization of mobile communications, and more particularly, to apparatuses and methods for Physical Broadcast Channel (PBCH) assisted synchronization during a Discontinuous Reception (DRX) operation.
Description of the Related Art
In a typical mobile communication environment, communications between a mobile device and a service network are performed arbitrarily according to the requests from or to the user of the mobile device. Since wireless transmission and reception are not necessarily performed at all times, keeping the mobile device always operating in transmission mode or reception mode causes unnecessary power consumption. For conserving battery power of the mobile device and saving wireless resources of the service network, a technique called Discontinuous Reception (DRX) operation is employed when there is no potential wireless transmission and reception for the mobile device in a forthcoming period of time. As shown in FIG. 1, in the OFF duration of the DRX operation, the service network does not page the mobile device and the mobile device enters a sleep mode in which at least the functionality of wireless transmission and reception is turned off. In the ON duration of the DRX operation, the mobile device wakes up from the sleep mode and turns on the functionality of wireless transmission and reception to operate in reception mode for monitoring possible paging from the service network.
However, due to the functionality of wireless transmission and reception being turned off in the sleep mode, the mobile device may become unsynchronized with the service network in the OFF duration of the DRX operation. That is, the timing drift and the frequency offset may increase too much for the mobile device to recover to be in-sync with the service network. Generally, the mobile device relies on pilot/reference signals to re-synchronize with the service network, but this inevitably results in an additional period of time for the mobile device to wake up from the sleep mode to receive the pilot/reference signals from the service network. Not to mention that, in some mobile communication systems, e.g., the Long Term Evolution (LTE) system, the time domain density of the pilot/reference signals is low, which prolongs the additional period of time required for re-synchronization.
Alternatively, it is proposed for the mobile device to re-do a cell search to acquire the timing and frequency information of the service network, after detecting that it is out-of-sync with the service network. Nonetheless, it takes a long time to finish a cell search, which not only consumes more power, but also impacts user experience.
In another conventional practice, it is proposed for the mobile device to employ a better crystal to maintain the timing drift and the frequency offset within an acceptable range when the mobile device is in the sleep mode. However, a better crystal capable of providing such an effect is expensive. As far as hardware cost is concerned, this practice has a significant drawback.
Thus, it is desirable to have a more power-efficient and cost-conserving way of solving the synchronization issue raised during the DRX operation.